In addition - Garmin let you input the whole post code - which limits the result to a street at most. TomTom only let you input all but the last 2 letters and then you have to put in the street name - which in rural areas is a massive zone and covers several villages - all with High Street as the name - for this reason I consider TomTom unfit for use.

tl/dr - Garmin good. TomTom useless.

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Now, I see that postcodes are good to use as once I learned that the English postcode gets you down to maybe 7 houses, it's way more precise than any other country postcode system, so I see Garmin as preferred in this case.